Condition control device and system

ABSTRACT

A solenoid operated device includes a camming linkage between the solenoid plunger and a member actuated thereby. This camming linkage is characterized to provide a reduced load on the plunger at its starting position and to increase the load as the plunger pulls in. The magnetic force on the moveable member increases as the moveable member moves in the direction of the electro-magnet. Motion transmitting means for causing movement of a power takeoff member, the initial movement being provided by the moveable magnetic member.

United States Patent [191 Harris [451 Nov. 13, 1973 [54] CONDITIONCONTROL DEVICE AND 2,434,070 1/1948 Gross 335/190 SYSTEM 1,176,9843/1916 Philpott 1 3,238,328 3/1966 Harris 335/64 [75] Inventor: John L.Harris, Clearwater, Fla.

[73] Assignee: Deltrol Corp., Bellwood, 111. j primary Examiner namldBroome i g 23 1972 Attorney-John L. Harris [21] App]. No.: 283,110

Related US. Application Data [57] ABSTRACT yi i n of r- 133,077, April1971. A solenoid operated device includes a camming link- 193,716,720-age between the solenoid plunger and a member actuated thereby. Thiscamming linkage is charac- [5?] }J.S. Cl. 335/63, 335/190 terized toprovide a d d l ad on the plunger at 2; its starting position and toincrease the load as the 335/189, 191, 255, 258 p-l-ungerPulvlsv-m' [56]uNlTE g gfzg gs gzqrENTs Claims, 3 Drawing Figures 2,911,494 11/1959Rigert 335/190 cmwue suamcs 65 1 MOTOR LATCH RIGIDLY 12 2 ATI'MHED ToRun sun LEVER 53 o 8 21 f 5...... s 9'9 J w menu! Pwo'rm MANUAL OPERATORPmmmunm Ian 3.772. 20

SOLENOID Wu. CURVE COMPRESSOR common (0| L m k c: I (2'2 commissolCKMMING SURFACE i; 77 RUN J 1 M070! 6| urrcu RIGIDLY 52 ATTACHED TO RUNsun Lave! I f 5 i \0 4 1 74 49 9* 86 k '3 FREELY PWOTEO so MAN UALOPERATOR CONDITION CONTROL DEVICE 'AND SYSTEM CROSS REFERENCE TO RELATEDAPPLICATIONS This application is a division of application Ser. No.133,077, filed Apr. 12, 1971, now U.S. Pat.- No. 3,716,720. I

BACKGROUND OF INVENTION This invention relates to automatic controls andmore particularly to time delay devices and control systems forprotecting electric motors such as refrigeration system compressors.

In the air conditioning and refrigeration industry it has become commonto install a time delay system between the compressor contactor and thethermostat and protective controls..The purpose is to prevent damage tothe compressor by short cycling due tothe safety controls responding toexcessive high or low pressures caused by a malfunctioning system. Suchtime delays also protect against frequency stops and starts bythermostat jiggling, and. insure a delay between. stopping andrestarting long enough to allow the pressures in the system to equalizeso the compressor starts in an un.-

loaded condition. Timershave also been used in compressor controlsystems for shunting out the high and low pressure controls for a shortperiod of time when the compressor first. starts. This is done to givetime for surges in the'system to settle down. This avoids false stops ofthe compressor and thus reduces the number of starts required.

Prior to applicants invention, the delay mechanism required a timer and.at least one relay. Also a separate timer was required to give the surgesettling period, and the system required a considerable amount ofelectrical connections between the various components.

One problem encountered with prior art systems is testing of thesystem.The usual. time cycle is on the order of five minutes. In the factoryoron service calls, this requires waste of considerable time. A manualoverride is needed and this must be one that can't be left in an unsafecondition.

Another problem isthe wide variation of voltages encountered. Some areashave 208 volt service while oth-- ers have 240 volt service. Thesevoltages can vary percent either way. It is desirable from an inventorystandpoint to have a single unit usable on both voltages. This requiressatisfactory performance over a range from 187 to 264 volts. Whereacontrol includes a sole-' noid, this voltage range gets into a problemofunderpower at the low voltage and overheating at the'high voltage,requiring an oversize solenoid for the low voltage and specialinsulation for the high voltage.

BRIEF SUMMARY OF INVENTION The timer runs for 15 seconds-and closes thecontactor switch which is now held closed by a latch.

The switch consists of two blades lifted by a single cam follower withcontacts disengaged. The blades are then released by the timer cam andthe latch holds one blade up to maintain the contacts engaged.

The timer continues to run for another 15 seconds during which time thestalling lug on the gear blocks out the solenoid lever, keeping thislever from being actuated by dropping. out of the solenoid. Thisprovides a minimum. run period allowing surges to settle down. Afterapproximately seconds the timer gear disengages from its drive pinionand the timer gear is stalled by a run stop.

When the thermostat is satisfied, it drops out the solenoid which: (1Releases the switch latch opening the switch to stop the compressor: (2)Releases the run stop allowing the timer gear to advance into engagementwith the drive pinion; and (3) Returns the standby stop him stallingposition. The timer then runs approximately five minutes and returns tothe standby position where the standby stop stalls it with the gearsdisengaged.

The solenoid operates the stops and latch through a compound levermechanism providing a long stroke for the solenoid. This compoundleverage also includes a camming action compensating for the non-linearforcestroke characteristic of the solenoid.

A manually operated lever is mounted on the latch pivot and has acamming surface lifting the inner switch blade to close the switchcontacts and lift the switch beyond the reach of the cam. When thesolenoid drops out to release the latch it also releases the manuallever.

One object of the invention is to provide a simple compact time delaymechanism in which the controlling functions are achieved mechanicallywith a minimum amount of components and electrical connections.

A further object is to provide a small compact unit operable over a widerange of line voltages.

Another object of the invention is to provide a manualoverride of thetime delay mechanism which is sim- BRIEF DESCRIPTION OF DRAWINGS FIG. 1is a schematic illustration of a combination timer and solenoid operatedcontrol mechanism embodying the invention.

FIG. 2 is a schematic wiring diagram of a typical airconditioning systemembodying the invention.

FIG. 3 is a typical solenoid stroke-force curve.

DETAILED DESCRIPTION OF INVENTION Referring to FIG. 1, referencecharacter 1 indicates an electric timing motor which drives a pinion 2in turn driving gear 3 carried by shaft 4 which also carries a pinion 5.The pinion 5 drives the main timing gear 6 carried by the main shaft 7which also carries a cam 8.

The cam 8 operates a switch generally indicated as 9 consisting ofswitch blades 10 and 11 which are anchored at their left hand ends as at12 and 13. The switch blade 11 is provided with a slot 14 and straddlesthe cam 8. The switch blade 11 carries a contact 15 and is provided withan extension 16. The switch blade 10 is formed with a slot 18 andcarries a molded plastic cam follower 19. This follower includes adownwardly extending hook portion 20 which extends around the right handend of blade 18 and bears on the bottom of this blade. The cam follower19 also includes a horizontal portion 21 extending parallel with theblade along the top thereof and merging with a downwardly extendingportion 22. The downward extension 22 passes through the slot 14 inswitch blade 11 and then extends to the right along the bottom of blade11 for lifting the same. As shown in the drawing, the extension 22passes freely through the slot 14 in the blade and includes the corner23 which serves a a cam follower surface riding the periphery of the cam8. The cam follower 19 also includes an inclined supporting surface 24extending under the lower edge of blade 10 adjacent the right hand edgeof the slot 18. The cam follower 19 is molded of a suitable flexiblematerial allowing it to be snapped into place on the switch blade 10without any other fastening means.

The gear 6 is of the mutilated type having two portions 26 and 27 inwhich the gear teeth are omitted. The gear 6 also includes a standbystop lug 28 and arun stop lug 29 which extend from the front face ofthergear as seen in the drawing. The cam shaft 7 also carries a startercam 30 which cooperates with a starter cam follower 31 which is pivotedat 32 and is biased against the cam by a spring 33. This starter cam isformed with two sloping drop-off portions 34 and 35. The cam is alsoformed with two rise portions 36 and 37.

A solenoid operated lever 40 is pivoted at 41 and has a leg 42 whichextends to the left of pivot 41 and downwardly into the path of thestalling lug 28.

The lever also has a downwardly extending leg 44 carrying an abutment 45which extends forwardly as seen in the drawing.

Mounted on a pivot 47 which is spaced from pivot 41 is a second lever48. This lever extends downwardly and is attached to the plunger 49 of asolenoid or electro-magnet generally indicated as 50. This solenoidincludes a bobbin 51 supporting a coil 52 and fitting inside a C frame53,. The plunger 49 is of magnetic material and extends into the centercore of the bobbin. A suitable backstop 54 is attached to the fram 53.The backstop, frame and plunger provide a magnetic path serving to pullthe plunger 49 to the left when the coil 52 is energized. ThisenergiZation of the solenoid coil 52 serves to cause rotation of thelever 48 in a clockwise direction about its pivot 47.

The lever 48 is formed with a driving surface 56 which bears against adriven surface 57 formed on the edge of lever 40. It will be apparentthat upon energiza tion of the coil 52 and rotation of the lever 48clockwise, the engagement of surfaces 56 and 57 will cause clockwiserotation of the lever 40 about its pivot 41.

The lever 40 is a power take-off member from the solenoid and isprovided with a biasing spring 60 tending to rotate this levercounterclockwise about pivot 41. This maintains the driven surface 57 oflever 40 in engagement with the driving surface 56 of lever 48. Thus,when the solenoid coil 52 is deenergized, spring 60 is free to rotatelever 40 counterclockwise which in turn rotates lever 48counterclockwise toward engagement with a stop 61.

The lever 40 also actuates a switch generally indicated as 63. Thisswitch includes a switch blade 64 which is anchored at its left hand endas at 65 and carries a contact 66 cooperating with a stationary contact67. The switch blade 64 extends alongside the lever 40 and is actuatedby a pin 68 carried on this lever. The switch blade 64 is biasedupwardly tending to cause contact 66 to engage contact 67. However, whenthe solenoid 50 is deenergized and the lever 40 is rotated to itscounter clockwise limit of rotation by the biasing spring 60, the pin 68on the lever pulls the switch blade 64 down for disengaging contact 66.When the solenoid is energized, it rotates lever 40 clockwise, thusraising the pin 68 and allowing contact 66 to engage contact 67.

A run stop surface 70 is carried on a run stop lever 71 which is pivotedon a shaft diagrammatically illustrated as 72. The shaft 72 also carriesa latch 73 having a latching surface 74. The latch 73 is provided with aspring 75 tending to rotate this latch into latching engagement with theextension 16 of switch blade 11. The run stall lever 71 and the latch 73are shown as two separate parts for illustrative purposes only.Preferably, these parts are molded in one piece. The run stall lever 70is formed with a driven surface 77 adjacent the pin 45 carried on lever40. When the solenoid 50 is deenergized and lever 40 is in the positionshown, the pin 45 has engaged the driven surface of lever 70 causing itto assume the position shown in which the stalling surface 70 is out ofthe path of the abutment 29 on the gear 6. This motion of lever 71 hasalso moved the latch 73 to releasing position in which the contacts ofswitch 9 are open. This same motion of the lever 71 has also caused thelower leg of the latch 73 to engage a stop 79. The pin 45 engagingdriven surface of lever 71 and the engagement of the latch 73 with thestop 79 serves as a stop for limiting the counterclockwise rotation oflever 40. It should be noted that the standby abutment 28 on the gear 6is at a greater distance from center than the run abutment 29. It isimportant that the counterclockwise limit of rotation of lever 40 belimited so that it never gets in the path of the run abutment 29 on thegear.

Mounted loosely on the shaft 72 supporting the run stall lever 71 andthe latch 73 is a manually operated lever 81. This lever includes ahandle portion 82 which should extend outside of the enclosure (notshown) in which the mechanism is located. The manual lever 81 is mountedbeside the latch 73 and under the extension 16 of switch blade 11. Thislatch includes a camming surface 83 and a holding surface 84..Thisholding surface 84 is preferably defined by a radius centered on thecenter of shaft 72. A stop 85 limits rotation of the lever 81 in theclockwise direction.

FIG. 2 shows schematically the wiring diagram for a typicalair-conditioning system embodying the invention. The primary of atransformer is connected across line wires L1 and L2 in series with thesafety controls 91 and 92. These safety controls may include a highpressure cut-out, a low pressure cut-out, and overload cut-out, etc. Thesecondary of the transformer 90 supplies current to the coil 52 of thetimer solenoid in series with a room thermostat 93. The timer motor 1 iswired across the transformer secondary so as to run continuously as longas power is supplied to the transformer 90. While it is preferable toemploy a low voltage thermostat, if desired, a line voltage thermostatmay be used. In such event, the transformer 90 may be omitted and linevoltage power from the safety controls applied directly to the timermotor and solenoid. This,of course, would require different windings forthe timer motor and solenoid.

Switches 9 and 63 are connected in parallel to the line wire L1. Switch9 controls the power to the compressor contactor coil 94 while switch 63controls power to the blower motor 95. The compressor contactor coilcontrols contacts Cl and C2 controlling power to the compressor motor96.

OPERATION With the parts in the position shown, the control isin thestandby position awaiting a call for cooling by the thermostat 93.Switch 9 is open thu's deenergizing the compressor contactor coilcausing switches C1 and C2 to be open and the compressor thereforedeenergized. Switch 63 is also open so that the blower 95 isdeenergized. Assuming the safety controls 91 and 92 are closed power issupplied to the transformer 90 and the timer motor 1 is running.However, the gear 6 is now positioned with the toothless portion 26adjacent the pinion 5, thus the motor 1 in an unloaded condition. Atthis time the starter cam follower 31 is pressing against the downwardsloping portion 34 of the starter cam 30. This is applying a torque tothe cam shaft or timing means tending to rotate it in a counterclockwisedirection. This motion, however is restrained by the standby stallingsurface 43 being in the path of the stalling lug 28 on gear 6. The lever40 is in stalling position due to the solenoid 50 now being deenergized.

When the thermostat or external condition responsive means 93 calls forcooling, it energizes the solenoid coil 52 pulling the plunger 49 to theright, thus causing lever 48 to rotate lever 40 clockwise through thecamming surface 57 of this lever. This movement releases the stallingmeans or surface 43 from abutment 28 of the driven gear 6. The startercam follower 31 acting on surface 34 is now free to advance the timingmeans 6-8 in a counterclockwise direction bringing the teeth of gear 6into mesh with the pinion 5. The gear 6 and cam 8 are now driven by themotor 1 in a counterclockwise direction. The cam follower 19 carried byswitch blade 10 is now raised by the cam 8 thus lifting switch blades 10and 11 with the contacts separated. As the cam follower approaches thetop of its stroke the extension 16 on switch blade 11 clears thelatching surface 74 of latch 73. At this time the abutment 45 carried bylever 40 is to the left and clear of surface 77 of the run stall lever71. The run stall lever 71 and'latch 73 are therefore free to be movedin a counterclockwise direction by spring 75. The latching surface 74 oflatch 73 therefore becomes positionedv beneath the extension 16 of theswitch blade 11. Also the stalling surface -70 moves into the path ofthe run stall lug 29 on gear 6. When the cam follower 19 is droppedbythe lobe 98 of cam 8, both switchblades l0 and 11 are free to drop.The extension 16 of blade 11 now is supported by the latching surface 74of latch 73. The contacts now engage before the cam follower 19 drops tothe lower surface 99 of the cam 8. Preferrably the cam speed andconfiguration is designed so that an interval of approximately secondselapses between the time the solenoid is first energized and the switch9 closes. As the blower switch 63 closed immediately when the solenoidwas energized, this gives a period of time for the blower to remove hotair from the condenser before the compressor is started.

After switch 9 closes for starting the compressor, the gear 6 continuesto be driven by the pinion 5 and the starter cam follower 31 rides upthe sloping surface 37 on the cam 30 thus storing power in the spring33. Approximately 90 seconds after switch 9 closes, the cam follower 31starts down the sloping portion 35 of cam 30. At approximately the sametime the toothless section 27 of gear 6 approaches the pinion 5 thusreleasing the gear from pinion 5. The cam shaft assembly is now drivenforward by the cam follower 3 1, bringing the run abutment 29 on gear 6into engagement with the run stop on lever 71. The cam shaft assembly isnow stopped with the toothless section of the gear 6 in registry withthe pinion 5, thus allowing the timing mechanism to be stalled while themotor 1 continues to run unloaded. At this time, the cam follower 31 isstill on the sloping portion 35 of cam 30 and is urging rotation of thecamshaft assembly or timing means, such rotation being prevented by therun abutment 29 engaging the stalling surface 70.

The compressor will normally remain in operation until the thermostat 93is satisfied. When this occurs, the solenoid 50 is deenergized whichpermits the biasing spring 60 of lever 40 to rotate this levercounterclockwise, this in turn causing counterclockwise rotation of thelever 48 and outward movement of the solenoid plunger 49. This samemotion of lever 40 also caused the abutment 45 to move to the rightagainst the driven surface 77 of the run stall lever 71. This releasedthe stalling surface 70 from abutment 29 on gear 6 and simultaneouslyreleased the latch 73 allowing downward movement of switch blade 11 foropening the contacts of switch 9. This deenergized the compressorcontact coil 94 which in turn deenergized the compressor 96. Due to thestalling surface 70 being released, the starter cam follower 31 actingon sloping portion 35 caused rotation of the cam shaft assembly forbringing gear 6 back into engagement with the pinion 5. The timingmechanism will now run back to the standby position where the parts arestalled by the standby stalling surface 43 being engaged by the standbyabutment 27 on gear 6. At this time the latch 83 is locked in unlatchedposition by engagement of the blade extension 16 with the drop-offportion of the latch. This holds the run stall lever in the outerposition as shown where it cannot interfere with the passage of thestandby abutment 28 on gear 6. Thus if the solenoid 50 should becomeenergized during the four minute 45 second resetting cycle of the timer,the run stall 70 will nevertheless be held clear of the standby abutment28.

It should be noted that when the thermostat first calls for cooling, itenergizes the solenoid 50 which rotates the lever 40 clockwise forreleasing the standby stop 43 from the standby abutment 28. This allowsinstant rotation of the timing means or cam shaft assembly and bringsthe outer edge of the run abutment 28 under the lower surfaceof lever40. This temporarily locks the safety controls 91 and 92 and thethermostat 93 out of control relationship over the compressor. Even ifthese controls opened their circuits and deenergized the solenoid 50,the lever 40 is maintained in its raised position so that the abutment45 is spaced from driven surface 77 of run stall lever 71 so as to allowthe latch 73 to move into place and cause closure of switch 9. Thestandby abutment 28 and the lower edge of lever 40 are arranged so as torequire approximately 30 seconds for the abutment 28 to clear the lever40, and place it back under the control of the condition responsivedevices. 15 seconds of this 30 second interval is taken up in closingthe switch 9 to start the compressor. This means that the compressormust now run at least 15 seconds irrespective of the safety controls 91and 92. This minimum on period prevents false stopping of the compressordue to surges occuring when the compressor first starts. The conditionresponsive devices are locked out mechanically by the timing mechanismfor sufficient time to allow the surges to settle down. These controlsare then placed back into full control so that the compressor can bestopped instantly if an unfavorable condition occurs.

The purpose of the compound leverage system including levers 48 and 40is to obtain more useful work from the solenoid and to make it operableover a wide voltage range. FIG. 3 shows a typical force-to-stroke curvefor a solenoid of the type illustrated. This curve indicates thesolenoid will pull approximately 10 ounces when the plunger is 0.5inches from its seated position. As the plunger comes in, the forceincreases to approximately ounces at 0.2;inches stroke. As the plungercontinues its inward motion the force available rapidly increases havingapproximately 35 ounces pull when the plunger is seated.

The use of the compound lever system makes it possible to utilize a longstroke on the solenoid without excessive movement of the lever 40. Alsowith the camming surface 57 on lever 40 the ratio of motion of lever 40relative to plunger travel is arranged to take advantage of thenon-linear force characteristic of the solenoid. With the cammingsurface illustrated, initial movement the solenoid plunger from itsretracted position results in relatively small movement of the lever 40against the action of its biasing spring 60. Thus the outward pull onthe solenoid is at a minimum corresponding with the force available fromthe solenoid at that position. AS the solenoid plunger movesin, theslope of the camming surface contacted by the portion 50 of lever 48increases thus increasing the movement of lever or power take-off member40, taking advantage of the increasing pull-available as the solenoidpulls in.

It should be noted that any time after abutment 28 clears the lever 40,the latch 73 can be released by deenergizing of the solenoid for openingthe switch 9. Once the latch has been released and the switch opened theswitch will remain open until the timer returns to the starting positionwhere latch 73 comes back into place and the cam follower 23 rides offlobe 98 of cam 8. This insures that the compressor cannot be started toooften, and that its operation will always be delayed until the pressuresin the system equalize so that the compressor can start in an unloadedcondition. This is very desirable except when the system is being testedeither on initial installation or during a service call. Hence themanual override is provided. When it is desired to start this systemmanually the thermostat 93 is turned up so as to energize the solenoid50 thus rocking lever 40 and moving the abutment 45 away from the runstall lever 71. The handle 82 on the manual lever 81 is now raised,bringing the camming surface 74 into engagement with the end of switchblade 11 thus raising this blade. This engages the contacts closingswitch 9 and starting the compressor. On continued movement of the lever82, the switch blade 11 is raised high enough to lift the cam follower19 sufficiently to be clear of the cam at its highest portion. Continuedrotation of the manual lever brings the circular portion 84 beneath theextension 16 of switch blade 11. Now there is no returning force on themanual lever and it will stay in the on position indefinitely. When themanual lever 81 is rotated counterclockwise and after the bladeextension 16 has been lifted clear of the latching surface on latch 74,the latch will move into latching position under extension 16 due to thebiasing spring 75. At this time due to the solenoid being energized, theabutment 45 is clear of the run stall lever which allows this movementof the latching position.

The compressor will now remain in operation until the thermostat 93 isreset or until the room temperature is reduced to the setting of thethermostat. Opening of the thermostat circuit drops out the solenoid 50allowing counterclockwise rotation of lever 40 under the acting ofbiasing spring 60. The abutment 45 on lever 40 moving to the right rocksthe run stall lever clockwise which also causes clockwise rotation ofthe latch 73. In its releasing motion latch 73 engages the pin 86 on themanual override lever 81 thus causing clockwise rotation of this leverinto the released position shown.

The manual override lever can also be operated without first energizingsolenoid 50. In this case rotation of the lever first lifts the lowerblade 1 1 until the extension 16 is raised above the latching surface 74on latch 73. After this occurs the pin 86 on the override lever engagesthe back of the latch and rotates it into latching position against theyielding action of the abutment 45 on the run stall lever 71. In otherwords manual operation of the manual override lever overcomes the spring60. However now when the manual override lever is released, the spring60 will move latch 73 to released position which in turn moves themanual override lever to released position.

From the foregoing it will be seen that the manual override lever may beused in twodifferent ways. In one case by turning the thermostat down toenergize the solenoid, the manual lever can be released after thecompressor is started and the compressor will run until the solenoid isdeenergized. In the other method the manual lever can be operatedwithout closing the thermostat circuit. However in this case the manuallever must be held in actuated position as long as operation of thecompressor is required. In no event, is it possible to manually lock outthe control system causing a dangerous situation if forgotten.

As numerous modifications may be made without departing from the spiritand scope of the invention it is desired to be limited only by the scopeof the appended claims.

I claim:

1. In an electro-magnetically actuated device, an electro-magnet havinga coil, an open magnetic path and a movable member of magnetic materialarranged to move in a direction closing said path in response toenergization of the coil, the magnetic force on the movable magneticmember increasing as said member moves in said direction, a powertake-off member, motion transmitting means for causing movement of thepower take-off member by power provided by the movable magnetic member,means providing a normal starting position for the movable magneticmember providing a predetermined open magnetic path, means providing anormal terminal position for the movable magnetic member, said movablemagnetic member being arranged normally to move from the startingposition to the terminal position in response to energization of thecoil, said motion transmitting means being constructed and arranged toincrease the relative rate of movement of the power take-off memberrelative to the rate of movement of the movable magnetic member. as saidmovable magnetic member moves from its normal starting position towardits normal terminal position, said motion transmitting means also beingconstructed and arranged to provide a substantially smaller relativerate of movement of the power take-off memher when the movable magneticmember is at its starting position than provided as said movable memberapproaches its terminal position.

2. A device as specified in claim 1 in which the motion transmittingmeans includes a camming surface which is contacted at different pointsas the movable magnetic member moves from its starting position to itsterminal position.

3. A device as specified in claim 2 in which the motion transmittingmeans comprises a first lever operated by the movable member and asecond lever, said levers being pivoted at spaced points, the cammingsurface being associated with one of said levers.

4. A device as specified in claim 3 in which the second lever isprovided with biasing means urging it against the first lever, thebiasing means acting through the camming surface to urge the movablemagnetic member in a direction opening the magnetic path.

1. In an electro-magnetically actuated device, an electro-magnet havinga coil, an open magnetic path and a movable member of magnetic materialarranged to move in a direction closing said path in response toenergization of the coil, the magnetic force on the movable magneticmember increasing as said member moves in said direction, a powertake-off member, motion transmitting means for causing movement of thepower take-off member by power provided by the movable magnetic member,means providing a normal starting position for the movable magneticmember providing a predetermined open magnetic path, means providing anormal terminal position for the movable magnetic member, said movablemagnetic member being arranged normally to move from the startingposition to the terminal position in response to energization of thecoil, said motion transmitting means being constructed and arranged toincrease the relative rate of movement of the power take-off memberrelative to the rate of movement of the movable magnetic member as saidmovable magnetic member moves from its normal starting position towardits normal terminal position, said motion transmitting means also beingconstructed and arranged to provide a substantially smaller relativerate of movement of the power take-off member when the movable magneticmember is at its starting position than provided as said movable memberapproaches its terminal position.
 2. A device as specified in claim 1 inwhich the motion transmitting means includes a camming surface which iscontacted at different points as the movable magnetic member moves fromits starting position to its terminal position.
 3. A device as specifiedin claim 2 in which the motion transmitting means comprises a firstlever operated by the movable member and a second lever, said leversbeing pivoted at spaced points, the camming surface being associatedwith one of said levers.
 4. A device as specified in claim 3 in whichthe second lever is provided with biasing means urging it against thefirst lever, the biasing means acting through the camming surface tourge the movable magnetic member in a direction opening the magneticpath.